Capacitive filtered feedthrough array for an implantable medical device

ABSTRACT

A capacitive filtered feedthrough assembly is formed in a solid state manner to employ highly miniaturized conductive paths each filtered by a discoid capacitive filter embedded in a capacitive filter array. A non-conductive, co-fired metal-ceramic substrate is formed from multiple layers that supports one or a plurality of substrate conductive paths and it is brazed to a conductive ferrule, adapted to be welded to a case, using a conductive, corrosion resistant braze material. The metal-ceramic substrate is attached to an internally disposed capacitive filter array that encloses one or a plurality of capacitive filter capacitor active electrodes each coupled to a filter array conductive path and at least one capacitor ground electrode. Each capacitive filter array conductive path is joined with a metal-ceramic conductive path to form a feedthrough conductive path. Bonding pads are attached to the internally disposed ends of each feedthrough conductive path, and corrosion resistant, conductive buttons are attached to and seal the externally disposed ends of each feedthrough conductive path. A plurality of conductive, substrate ground paths are formed extending through the co-fired metal-ceramic substrate between internally and externally facing layer surfaces thereof and electrically isolated from the substrate conductive paths. The capacitor ground electrodes are coupled electrically to the plurality of conductive, substrate ground paths and to the ferrule.

FIELD OF THE INVENTION

[0001] This invention relates to electrical feedthroughs of improveddesign and to their method of fabrication, particularly for use withimplantable medical devices.

BACKGROUND OF THE INVENTION

[0002] Electrical feedthroughs serve the purpose of providing anelectrical circuit path extending from the interior of a hermeticallysealed case or housing to an external point outside the case.Implantable medical devices (IMDs) such as implantable pulse generators(IPGs) for cardiac pacemakers, implantable cardioverter/defibrillators(ICDs), nerve, brain, organ and muscle stimulators and implantablemonitors, or the like, employ such electrical feedthroughs through theircase to make electrical connections with leads, electrodes and sensorslocated outside the case.

[0003] Such feedthroughs typically include a ferrule adapted to fitwithin an opening in the case, one or more conductor and anon-conductive hermetic glass or ceramic seal which supports andelectrically isolates each such conductor from the other conductorspassing through it and from the ferrule. The IMD case is typicallyformed of a biocompatible metal, e.g., titanium, although non-conductiveceramics materials have been proposed for forming the case. The ferruleis typically of a metal that can be welded or otherwise adhered to thecase in a hermetically sealed manner.

[0004] Typically, single pin feedthroughs supported by glass, sapphireand ceramic were used with the first hermetically sealed IMD cases forIPGs. As time has passed, the IPG case size has dramatically reduced andthe number of external leads, electrodes and sensors that are to becoupled with the circuitry of the IPG has increased. Consequently, useof the relatively large single pin feedthroughs is no longer feasible,and numerous multiple conductor feedthroughs have been used or proposedfor use that fit within the smaller sized case opening and provide two,three, four or more conductors.

[0005] Many different insulator structures and conductor structures areknown in the art of multiple conductor feedthroughs wherein theinsulator structure also provides a hermetic seal to prevent entry ofbody fluids through the feedthrough and into the housing of the medicaldevice. The conductors typically comprise electrical wires or pins thatextend through a glass and/or ceramic layer within a metal ferruleopening as shown, for example, in commonly assigned U.S. Pat. Nos.4,991,582, 5,782,891, and 5,866,851 or through a ceramic case as shownin the commonly assigned '891 patent and in U.S. Pat. No. 5,470,345. Ithas also been proposed to use co-fired ceramic layer substrates that areprovided with conductive paths formed of traces and vias as disclosed,for example, in U.S. Pat. Nos. 4,420,652, 5,434,358, 5,782,891,5,620,476, 5,683,435, 5,750,926, and 5,973,906.

[0006] Such multi-conductor feedthroughs have an internally disposedportion configured to be disposed inside the case for connection withelectrical circuitry and an externally disposed portion configured to bedisposed outside the case that is typically coupled electrically withconnector elements for making connection with the leads, electrodes orsensors. The elongated lead conductors extending from the connectorelements effectively act as antennae that tend to collect strayelectromagnetic interference (EMI) signals that may interfere withnormal IMD operations. At certain frequencies, for example, EMI can bemistaken for telemetry signals and cause an IPG to change operatingmode.

[0007] This problem has been addressed in certain of theabove-referenced patents by incorporating a capacitor structure upon theinternally facing portion of the feedthrough ferrule coupled betweeneach feedthrough conductor and a common ground, the ferrule, to filterout any high frequency EMI transmitted from the external lead conductorthrough the feedthrough conductor. The feedthrough capacitors originallywere discrete capacitors but presently can take the form of chipcapacitors that are mounted as shown in the above-referenced '891, '435,'476, and '906 patents and in further U.S. Pat. Nos. 5,650,759,5,896,267 and 5,959,829, for example. Or the feedthrough capacitors cantake the form of discrete discoidal capacitive filters or discoidalcapacitive filter arrays as shown in commonly assigned U.S. Pat. Nos.5,735,884, 5,759,197, 5,836,992, 5,867,361, and 5,870,272 and furtherU.S. Pat. Nos. 5,287,076, 5,333,095, 5,905,627 and 5,999,398.

[0008] These patents disclose use of discoidal filters and filter arraysin association with conductive pins which are of relatively large scaleand difficult to miniaturize without complicating manufacture. It isdesirable to further miniaturize and simplify the fabrication of themulti-conductor feedthrough assembly

[0009] Although feedthrough filter capacitor assemblies of the typedescribed above have performed in a generally satisfactory manner, themanufacture and installation of such filter capacitor assemblies hasbeen relatively time consuming and therefore costly. For example,installation of the discoidal capacitor into the small annular spacebetween the terminal pin and ferrule as shown in a number of thesepatents can be a difficult and complex multi-step procedure to ensureformation of reliable, high quality electrical connections.

[0010] Other problems have arisen when chip capacitors have been coupledto conductive trace and via pathways of co-fired multi-layermetal-ceramic substrates disclosed in the referenced '652, '358, '891,'476, '435, '926, and '906 patents. The conductive paths of thefeedthrough arrays and attached capacitors suffer from high inductancewhich has the effect of failing to attenuate EMI and other unwantedsignals, characterized as “poor insertion loss”.

[0011] A high integrity hermetic seal for medical implant applicationsis very critical to prevent the ingress of body fluids into the IMD.Even a small leak rate of such body fluid penetration can, over a periodof many years, build up and damage sensitive internal electroniccomponents. This can cause catastrophic failure of the implanted device.The hermetic seal for medical implant (as well as space and military)applications is typically constructed of highly stable alumina ceramicor glass materials with very low bulk permeability. The above-describedfeedthroughs formed using metal-ceramic co-fired substrates, however,have not been hermetic because the metal component of the substratecorrodes in body fluids, and the substrates have cracked from stressesthat developed from brazing and welding processes.

[0012] Withstanding the high temperature and thermal stresses associatedwith the welding of a hermetically sealed terminal with a premountedceramic feedthrough capacitor is very difficult to achieve with the'551, '095 and other prior art designs. The electrical/mechanicalconnection to the outside perimeter or outside diameter of thefeedthrough capacitor has a very high thermal conductivity as comparedto air. The welding operation typically employed in the medical implantindustry to install the filtered hermetic terminal into the IMD caseopening can involve a welding operation in very close proximity to thiselectrical/mechanical connection area. Accordingly, in the prior art,the ceramic feedthrough capacitors are subjected to a dramatictemperature rise. This temperature rise produces mechanical stress inthe capacitor due to the mismatch in thermal coefficients of expansionof the surrounding materials.

[0013] In addition, in the prior art, the capacitor lead connectionsmust be of very high temperature materials to withstand the high peaktemperatures reached during the welding operation (as much as 500 C.°).A similar, but less severe, situation is applicable in military, spaceand commercial applications where similar prior art devices are solderedinstead of welded by the user into a bulkhead or substrate. Many ofthese prior art devices employ a soldered connection to the outsideperimeter or outside diameter of the feedthrough capacitor. Excessiveand unevenly applied soldering heat has been known to damage such priorart devices. Accordingly, there is a need for a filter capacitor andfeedthrough array in a single assembly that addresses the drawbacksnoted above in connection with the prior art.

[0014] In particular, a capacitive filtered feedthrough array is neededthat is subjected to far less temperature rise during the manufacturethereof. Moreover, such an improvement would make the assemblyrelatively immune to the aforementioned stressful installationtechniques.

[0015] Moreover, a capacitive filtered feedthrough array is needed whichis of simplified construction, utilizing a straightforward anduncomplicated assembly, that can result in manufacturing costreductions. Of course the new design must be capable of effectivelyfiltering out undesirable EMI. The present invention fulfills theseneeds and provides other related advantages.

SUMMARY OF THE INVENTION

[0016] A capacitive filtered feedthrough assembly is formed inaccordance with the present invention in a solid state manner to employhighly miniaturized conductive paths each filtered by a discoidcapacitive filter embedded in a capacitive filter array. Anon-conductive, co-fired metal-ceramic substrate is formed from multiplelayers that supports one or a plurality of substrate conductive pathsand it is brazed to a conductive ferrule, adapted to be welded to acase, using a conductive, corrosion resistant braze material. Themetal-ceramic substrate is attached to an internally disposed capacitivefilter array that encloses one or a plurality of capacitive filtercapacitor active electrodes each coupled to a filter array conductivepath and at least one capacitor ground electrode. Each capacitive filterarray conductive path is joined with a metal-ceramic conductive path toform a feedthrough conductive path. Bonding pads are attached to theinternally disposed ends of each feedthrough conductive path, andcorrosion resistant, conductive buttons are attached to and seal theexternally disposed ends of each feedthrough conductive path. Eachcapacitor ground electrode is electrically coupled with the ferrule.

[0017] Preferably, a plurality of such feedthrough conductive paths areformed, and each capacitive filter comprises a plurality of capacitoractive and ground electrodes, wherein the capacitor ground electrodesare electrically connected in common.

[0018] Moreover, preferably, a plurality of conductive, substrate groundpaths are formed extending through the co-fired metal-ceramic substratebetween internally and externally facing layer surfaces thereof andelectrically isolated from the substrate conductive paths. The capacitorground electrodes are coupled electrically to the plurality ofconductive, substrate ground paths and to the ferrule.

[0019] In addition, preferably, the capacitive filter array conductivepaths are formed by solder filling holes extending through the filterarray substrate between internally and externally facing array surfacesthereof. The application of the solder also joins the externally facingarray surface with the internally facing metal-ceramic substrate layersurface and electrically joins the capacitive filter array conductivepaths with the metal-ceramic conductive paths to form the feedthroughconductive paths.

[0020] Utilization of an internally grounded, metal-ceramic substrateproviding a plurality of conductive substrate paths in stacked, aligned,relation to a capacitive filter array as disclosed herein provides anumber of advantages:

[0021] A hermetic seal is achieved by brazing a co-fired metal-ceramicsubstrate with low permeability to a metallic ferrule. The inventiveferrule-substrate braze joint design minimizes the tensile stresses inthe co-fired substrate, thus preventing cracking of the co-firedsubstrate during brazing and welding. In addition, the ferrule has athin flange which minimizes stress applied to the co-fired substrateduring welding. Corrosion of the co-fired metal phase of the substrateis prevented by protecting the exposed metal vias and pads withcorrosion resistant metallizations and braze materials.

[0022] Because the capacitive filter array is displaced from the ferruleand supported by the metal-ceramic substrate, the heat imparted to theferrule flange during welding causes minimal temperature elevation ofthe capacitive filter array, and does not cause damage to it.

[0023] The attachment of the conductive paths of the outward facingcapacitive filter surface to the metallized layers of the inward facingsurface of the metal-ceramic substrate using reflow soldering providessecure attachment and low resistance electrical connection andsimplifies manufacturing. The use of conductive epoxy compounds foradhesion is thereby avoided. Conductive epoxy adhesion layers can bridgethe non-conductive ceramic between adjacent conductive paths and causeelectrical shorts. And voids can occur in bridging the conductive pathsof the metal-ceramic substrate and the capacitive filter elements.

[0024] The reflow soldering attachment of the of the conductive paths ofthe outward facing capacitive filter surface to the metallized layers ofthe inward facing surface of the metal-ceramic substrate also isadvantageous in that the solder flow takes place in an oven underuniformly applied temperature to the entire assembly, thereby avoidingdamage that can be caused in hand soldering such parts together.

[0025] The capacitor ground electrodes of the discoidal capacitors ofthe capacitive filter array are electrically coupled together andthrough the plurality of substrate ground paths of the metal-ceramicsubstrate and then through the braze to the ferrule. The plurality ofsubstrate ground paths are selected in total cross-section area toprovide a total ground via cross-section area that minimizes theinductance of the filtered feedthrough assembly, resulting in favorableinsertion loss of EMI and unwanted signals.

[0026] Size of the feedthrough is decreased by eliminating the pins, thepin braze joints, and the welds between the pins. The pin-to-pin spacingof two single pin or unipolar feedthroughs is typically on the order of0.125 inches. The above-described capacitive filtered feedthrough arrayprovides a spacing of 0.050 inches between adjacent conductive paths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] These and other advantages and features of the present inventionwill be appreciated as the same becomes better understood by referenceto the following detailed description of the preferred embodiment of theinvention when considered in connection with the accompanying drawings,in which like numbered reference numbers designate like parts throughoutthe figures thereof, and wherein:

[0028]FIG. 1 is a perspective view of the filtered feedthrough assemblyof the present invention adapted to be fitted into an opening of a caseof a hermetically sealed electronic device showing the externallydisposed portion configured to be disposed outside and face outwardlyfrom the case;

[0029]FIG. 2 is a perspective view of the filtered feedthrough assemblyof the present invention adapted to be fitted into an opening of a caseof a hermetically sealed electronic device showing the internallydisposed portion configured to be disposed inside the case and faceinward;

[0030]FIG. 3 is a plan view looking toward the internally disposedportion of the filtered feedthrough assembly of the present invention;

[0031]FIG. 4 is a cross-section side view of the filtered feedthroughassembly taken along lines 4-4 of FIG. 3;

[0032]FIG. 5 is an expanded end portion of the cross-section view ofFIG. 4

[0033]FIG. 6 is a cross-section end view of the filtered feedthroughassembly taken along lines 6-6 of FIG. 3;

[0034]FIG. 7 is an exploded view of the components of the filteredfeedthrough assembly of FIGS. 1-6;

[0035]FIG. 8 is a perspective view of the filtered feedthrough assemblyof the present invention fitted into an opening of a half portion of thecase of a hermetically sealed electronic device showing the externallydisposed portion outside the case;

[0036]FIG. 9 is a perspective view of the filtered feedthrough assemblyof the present invention fitted into the opening of the case halfportion of FIG. 7 showing the internally disposed portion inside thecase and electrically connected to an electrical component;

[0037]FIG. 10 is a flow chart illustrating the steps of fabricating themulti-layer, co-fired metal-ceramic substrate adapted to be brazed withthe capacitive filter array formed in the steps of FIG. 11, the ferrule,and other components in the steps of FIG. 12;

[0038]FIG. 11 is a flow chart illustrating the steps of fabricating thecapacitive filter array adapted to be brazed with the co-firedmetal-ceramic substrate formed in the steps of FIG. 10, the ferrule, andother components in the steps of FIG. 12; and

[0039]FIG. 12 is a flow chart illustrating the steps of fabricating thefiltered feedthrough assembly from the capacitive filter array formed inthe steps of FIG. 11, the co-fired metal-ceramic substrate formed in thesteps of FIG. 10, the ferrule, and other components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0040] FIGS. 1-7 depict the filtered feedthrough assembly 10 adapted tobe fitted into an opening 204 of a case 202 of a hermetically sealedelectronic device 200 as shown in FIGS. 8 and 9 and manufactured inaccordance with the flow chart steps of FIGS. 10-12. The feedthroughassembly 10 has an internally disposed portion 12 configured to bedisposed inside the case 202 and an externally disposed portion 14configured to be disposed outside the case 202.

[0041] The filtered feedthrough assembly 10 shown in FIGS. 1-9 comprisesa electrically conductive ferrule 20 having a ferrule wall 22 with aninner wall surface 24 defining a centrally disposed ferrule opening 30and extending between opposed internal and external sides 26 and 28.When ferrule 20 is fitted into the case opening 204, the internallyfacing side 26 is adapted face toward the inside of the case 202, andthe externally facing side 28 is adapted face toward the exterior of thecase 202. The electrically conductive ferrule 20 further comprises arelatively thin welding flange 32 extending outwardly of the ferrulewall 22 away from the ferrule opening 30 for a predetermined distancedefining a flange width FW. The flange 32 is formed to have a relativelythin flange thickness FT for absorbing stress caused by thermal weldingenergy applied to the ferrule 20 in the process of welding the flange 32to the case 202 around the case opening 204 as shown in FIGS. 8 and 9.

[0042] The ferrule 20 is preferably formed of a conductive materialselected from the group consisting of niobium, titanium, titanium alloyssuch as titanium-6Al-4V or titanium-vanadium, platinum, molybdenum,zirconium, tantalum, vanadium, tungsten, iridium, rhodium, rhenium,osmium, ruthenium, palladium, silver, and alloys, mixtures andcombinations thereof. Niobium is the optimal material for forming theferrule 20 because it has a coefficient of thermal expansion (CTE) thatis compatible with the CTE of the substrate 40 so that heat-inducedduring brazing of the metal-ceramic substrate edge to the ferrule innerwall surface 24 does not damage the substrate 40.

[0043] The multi-layer, co-fired metal-ceramic substrate 40 shown indetail in FIGS. 5 and 7 has an internally facing major surface or side42 and an externally facing major surface or side 44 that are joined bya common substrate edge 46. The substrate 40 is dimensioned and shapedto fit within the ferrule opening 30 with the common substrate edge 46in close relation to the ferrule inner wall surface 24. The commonsubstrate edge 46 is brazed to the ferrule inner wall surface 24 using asubstrate-ferrule braze joint 48.

[0044] The metal-ceramic substrate 40 is formed of a plurality of planarceramic layers 52, 54, 56, 58 and 60. Each ceramic layer is shaped in agreen state to have a layer thickness and a plurality of via holesextending therethrough between an internally facing layer surface and anexternally facing layer surface. The co-fired metal-ceramic substrateceramic material comprises one of the group consisting essentially ofalumina, aluminum nitride, beryllium oxide, silicon dioxide, andglass-ceramic materials that has a CTE compatible with the CTE of thematerial of the ferrule.

[0045] A plurality (nine in the depicted example) of conductive paths,e.g. path 50 shown in FIGS. 5 and 6, extend through the layers 52-60 ofco-fired metal-ceramic substrate 40 and are electrically isolated fromone another by the ceramic material. Conductive path 50 (and all theother conductive paths) comprises a plurality of electrically conductivevias 62, 64, 66, 68 extending through the plurality of layer thicknessesand a like plurality of electrically conductive traces 72, 74 and 76formed on certain of the internally or externally facing layer surfacessuch that the conductive trace 72 joins the conductive vias 62 and 64,the conductive trace 74 joins the conductive vias 64 and 66, and theconductive trace 76 joins the vias 66 and 68 to form the conductive path50. The layer holes and vias 62-68 filling them are staggered in theelongated direction of the feedthrough assembly 10 as shown in FIGS. 4and 5 but are aligned in the narrow direction as shown in FIG. 6. Theconductive vias and traces are formed of a refractory metal, e.g.,tungsten, as described further in reference to FIG. 10.

[0046] A further plurality (twenty in the depicted example) of groundpaths 118 each comprising substrate ground paths 118 extending throughall layers 52-60 spaced apart around the periphery of the co-firedmetal-ceramic substrate 40. The ground paths 118 also comprise one ormore ground trace, e.g. ground plane traces or layers 132, 134 and 136shown in FIG. 5, extending peripherally along the substrate layersurfaces from the substrate ground paths 118 to the substrate edge 46.The ground trace 132 assists in making electrical contact with theground solder joint 130 and with the substrate-ferrule braze joint 48.The ground traces 134 and 136 extend to a metallization layer 140 formedover the substrate edge 46. The number of substrate ground paths 118substrate ground paths 118 formed in this manner is selected to providea total ground via cross-section area that minimizes the inductance ofthe filtered feedthrough assembly 10 resulting in favorable insertionloss of EMI and unwanted signals.

[0047] Each such conductive path 50 extends all the way through thesubstrate 40 between the internally facing side 42 and the externallyfacing side 44. On the externally facing side 44, ceramic layer 60 isformed in the green state with a plurality of button cavities 80 eachaligned with a via 68 of layer 58. A substrate conductor pad or button70 is fitted within each button cavity 80 of the layer 60 and adhered tovia 68 by a button braze joint 78 formed of gold or a nickel-gold alloy.The pads or bonding buttons 70 are preferably formed of a conductivematerial selected from the group consisting of niobium, platinum or aplatinum-iridium alloy, titanium, titanium alloys such astitanium-6Al-4V or titanium-vanadium, molybdenum, zirconium, tantalum,vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium,palladium, silver, and alloys, mixtures and combinations thereof. Inthis way, a plurality of externally disposed bonding buttons 70 aresupported along the externally disposed feedthrough portion 14, and eachexternally disposed bonding button 70 is electrically conducted with anelectrically conductive path 50 of the metal-ceramic substrate 40.

[0048] A substrate conductor plated pad 82 is formed of gold or a goldalloy on the internally facing surface of layer 52 and electricallycoupled to via 62. A solder layer 128 adheres to plated pad 82 duringassembly of the feedthrough assembly 10 described below with referenceto FIG. 12. The plurality of ceramic layers are shaped punched withholes, and printed with the traces and vias and assembled together inthe ceramic green state, and the assembly is then co-fired from thegreen state to form the substrate 40 as further described below inreference to FIG. 10.

[0049] The discoidal capacitive filter array 90 is formed of a ceramiccapacitive filter array substrate 92 having an internally facing filtersubstrate side 94 and an externally facing filter substrate side 96joined by a common filter substrate edge 98. The discoidal capacitorfilter array 90 is formed with a plurality of discoidal capacitivefilters, e.g., capacitive filter 100, that are electrically connectedwith a respective one of the substrate conductive paths, e.g.,conductive path 50, and provide a filtered electrically conductive pathbetween the internally disposed bonding pad 120 and the externallydisposed button 70. The number of conductive paths so formed can varyfrom the nine that are depicted in FIGS. 1-9.

[0050] The capacitive filter array substrate 92 is preferably formed oflayers of barium titanate and precious metal traces in the mannerdescribed below with reference to FIG. 11. The plurality of capacitivefilters 100 and the filter array conductive paths 110 associatedtherewith are formed in and electrically isolated from one another bythe ceramic material and extend between the internally facing filtersubstrate side 94 and the externally facing filter substrate side 96.Each filter array conductive path 110 is formed of melted solderpre-forms as described below that fill a respective capacitor filterhole 108 extending between the internally facing filter substrate side94 and an externally facing filter substrate side 96.

[0051] Each discoidal capacitive filter 100 comprises at least onecapacitor electrode formed within the filter substrate and extendingoutward from a filter array conductive path 110 in overlapping spacedrelation to at least one common ground plate. The number and dielectricthickness spacing of the capacitor electrode sets varies in accordancewith the capacitance value and the voltage rating of the discoidalcapacitor. The capacitor active and ground electrodes are formed ofsilver thick films, silver-palladium alloy thick films, orsilver-platinum alloy thick films disposed on inner capacitive filterlayer surfaces during the fabrication of the capacitive filter array 90.The number of capacitor active and ground electrodes, the sizes of eachand the spacing and overlapping relation can be varied for eachdiscoidal capacitive filter 100 within the capacitive filter array 90and between differing models of such capacitive filter arrays 90 totailor the filter characteristics to the circuitry of the particularIMD. In the depicted example, the capacitive filters 100 either havethree capacitor active electrodes 112, 114, 116 or two capacitor activeelectrodes 122, 124 that are spaced from three ground electrodes 102,104, 106 that extend inward from the filter substrate edge 98. Inoperation, the discoidal capacitor permits passage of relatively lowfrequency electrical signals along the conductive path it is coupledwith, while shielding and decoupling/attenuating undesired interferencesignals of typically high frequency.

[0052] The ground solder joint 130, preferably formed of solder or aconductive epoxy, adheres against a metallized layer 111 formed on thefilter substrate edge 98 as described below in reference to FIG. 12 thatelectrically connects the three capacitor ground electrodes 102, 104,106 together. The ground solder joint 130 also electrically connects thethree capacitor ground electrodes 102, 104, 106 to the ferrule 20through the conductive ground trace 132, the plurality of substrateground paths 118, and the substrate-ferrule braze joint 48. The groundsolder joint 130 can be formed of ABLEBOND.RTM.8700 electricallyconductive silver-filled epoxy adhesive provided by ABLESTIKLABORATORIES of Rancho Dominguez, Calif. Other suitable electricallyconductive glue or epoxy-based adhesives and other suitable materialsmay also be employed in the present invention to form the ground solderjoint 130. Such materials include gold or copper-filled epoxies, carbonor graphite-filled epoxies or even electrically conductive plasticsacting effectively as adhesive joints after their application and uponcooling, such as at least some of the electrically conductive plasticsor polymers disclosed in U.S. Pat. No. 5,685,632. The ground solderjoint 130 and the solder layers 128 mechanically join the externallyfacing filter substrate side to the internally facing substrate side.The solder layers 128 electrically join each filter array conductivepath 110 to a substrate conductor pad 82 of each substrate conductivepath 50.

[0053] The substrate-ferrule braze joint 48 is preferably formed of99.9% or purer gold or a nickel-gold alloy that adheres to themetallization layer 140 on substrate edge 46 and to the ferrule wall 22and provides a hermetic seal of the ferrule 20 with the metal-ceramicsubstrate 40. The substrate-ferrule braze joint 48 may also be formedof: (a) gold alloys comprising gold and at least one of titanium,niobium, vanadium, nickel, molybdenum, platinum, palladium, ruthenium,silver, rhodium, osmium, indium, and alloys, mixtures and thereof; (b)copper-silver alloys, including copper-silver eutectic alloys,comprising copper and silver and optionally at least one of indium,titanium, tin, gallium, palladium, platinum, and alloys, mixtures andcombinations thereof; and (c) silver-palladium-gallium alloys.

[0054] The filtered feedthrough assembly 10 thus provides a plurality ofminiaturized, electrically isolated, and capacitively filtered,electrical conductors formed of conductive path 50 and 110 extendingbetween a respective internal bonding pad 120 of the internally disposedportion 12 and bonding button 70 of the externally disposed portion 14when the feedthrough assembly 10 is affixed into an opening 204 in thecase 202 of the electronic device, e.g., the IMD 200 of FIGS. 8 and 9.The case 202 for an IMD is preferably fabricated of titanium, and theferrule flange 32 is welded thereto. The ferrule 20 is preferably formedof niobium because niobium has a comparable CTE to the CTE of AlO₂ whichis a preferred substrate ceramic material. However, the ferrule may beformed of titanium, titanium alloys such as titanium-6Al-4V ortitanium-vanadium, platinum, molybdenum, zirconium, tantalum, vanadium,tungsten, iridium, rhodium, rhenium, osmium, ruthenium, palladium,silver, and alloys, mixtures and combinations thereof.

[0055]FIG. 10 is a flow chart illustrating the steps of fabricating themulti-layer, co-fired metal-ceramic substrate 40 adapted to be brazedwith the capacitive filter array 90 formed in the steps of FIG. 11, theferrule 20, and other components in the steps of FIG. 12. In step S100the ceramic layers 52-60 are preferably tape cast from conventionalceramic or low temperature co-fired ceramic, such as alumina, aluminumnitride, beryllium oxide, silicon dioxide, etc., that has a CTEcompatible with the CTE of the material of the ferrule 20. Preferably,88%-96% pure alumina (AlO₂) is tape cast using conventional “greensheet” techniques on glass-ceramic or MYLAR support materials. Ingeneral, such techniques start with a ceramic slurry formed by mixing aceramic particulate, a thermoplastic polymer and solvents. This slurryis spread into ceramic sheets of predetermined thickness, typicallyabout 0.006-0.010 inches thick, from which the solvents are volitized,leaving self-supporting flexible green sheets.

[0056] In step S102, the holes that will be filled with conductivematerial to form the vias 62-68 of each conductive path 50 and thealigned ground vias, as well as the button cavities 80 of the layer 60are made, using any conventional technique, such as drilling, punching,laser cutting, etc., through each of the green sheets from which theceramic layers 52-60 are formed. The vias 42 may have a size appropriatefor the path spacing, with about a 0.004 inch diameter hole beingappropriate for 0.020 inch center to center path spacing.

[0057] In step S104, the via holes are filled with a paste of refractorymetal, e.g., tungsten, molybdenum, or tantalum paste, preferably usingscreen printing. In step S104, the conductive traces, e.g. traces 72,74, 76, are also applied to particular surface areas of the ceramiclayers 52-60 over the vias. The traces may comprise an electricalconductor, such as copper, aluminum, or a refractory metal paste, thatmay be deposited on the green sheets using conventional techniques. Thetraces may be deposited, sprayed, screened, dipped, plated, etc. ontothe green sheets. The traces may have a center to center spacing assmall as about 0.020 inch (smaller spacing may be achievable as traceforming technology advances) so that a conductive path density ofassociated vias and traces of up to 50 or more paths per inch may beachieved.

[0058] In these ways, the via holes are filled and the conductive tracesare applied to the green sheets before they are stacked and laminated instep S106 using a mechanical or hydraulic press for firing. The stackedand laminated ceramic layers are trimmed to the external edge dimensionssufficient to fit within the ferrule opening, taking into account anyshrinkage that may occur from co-firing of the stacked layers. In stepS110, the assembly of the stacked, laminated and trimmed green sheets isco-fired to drive off the resin and sinter the particulate together intoa multi-layer metal-ceramic substrate 40 of higher density than thegreen sheets forming the layers 52-60. The green sheets shrink inthickness when fired such that a 0.006 inch thick green sheet typicallyshrinks to a layer thickness of about 0.005 inch. The green sheets maybe fired using conventional techniques, with low temperature co-firedceramic techniques being recommended when copper or aluminum are used.

[0059] In step S112, the outer edge 46 and the inward and outward facingsubstrate surfaces 42 and 44 are machined and polished to size andfinish specifications. Then, in step S114, the various regions of theoutward facing surface 44 are metallized to form the button braze joints78 for each conductive path 50 and the band-shaped, ground plane layer136 electrically connecting all of the substrate ground paths 118together at the outward facing ends thereof. The substrate edge 46 isalso metallized with metallization layer 140. These metallization layersare preferably sputtered films of niobium, titanium, tungsten,molybdenum or alloys thereof. The machining and polishing of the outeredge 46 which is then metallized improves the dimensional tolerances ofthe co-fired substrate 40 which in turn enables the reliable use of thesubstrate-ferrule braze joint 48 that is formed in step S300 of FIG. 12.

[0060] In a preferred embodiment of the present invention, where puregold is employed to form the substrate-ferrule braze joint 48, a 25,000Angstrom thick layer of niobium is preferably sputtered onto substrateedge 46 and on edge bands of the inward facing surface 44 to form theband-shaped, ground plane or trace layers 132 and 136 by vacuumdeposition using a Model No. 2400 PERKINELMER.RTM. sputtering system.The niobium layer is most preferably between about 15,000 and about32,000 Angstroms thick. These metallization layers may not be requiredif metals such as: (i) gold alloys comprising gold and at least one oftitanium, niobium, vanadium, nickel, molybdenum, platinum, palladium,ruthenium, silver, rhodium, osmium, iridium., and alloys, mixtures andthereof; (ii) copper-silver alloys, including copper-silver eutecticalloys, comprising copper and silver and optionally at least one ofindium, titanium, tin, gallium, palladium, platinum; or (iii) alloys,mixtures or combinations of (i) or (ii) are employed for thesubstrate-ferrule braze joint 48.

[0061]FIG. 11 is a flow chart illustrating the steps of fabricating thecapacitive filter array 90 adapted to be brazed with the co-firedmetal-ceramic substrate 40 formed in the steps of FIG. 10, the ferrule20, and other components in the steps of FIG. 12. The capacitive filterarray 90 is also formed of layers of ceramic material, preferably bariumtitanate, and screen printed, conductive, capacitor active and groundelectrodes that are co-fired to form a monolithic structure.

[0062] In step S200, the barium titanate ceramic layers are tape cast,and the capacitor active and ground electrodes are screen printed on thesurfaces thereof in step S202. The capacitor electrodes are formed ofsilver thick films, silver-palladium alloy thick films, orsilver-platinum alloy, thick films. The layers are stacked and laminatedusing a mechanical or hydraulic press in step S204, and the stacked andlaminated layers are machined and drilled to form the capacitorconductive path receiving, capacitive filter holes 108 in steps S206 andS208.

[0063] The partly completed capacitor filter array 90 is fired in stepS210 to form the monolithic structure. Then, in steps S212 and S214, theedges of the active capacitive filter electrodes 112, 114, 116 or 122,124 exposed by the capacitor holes 108 and the capacitive filter groundelectrodes 102, 104 and 106 are coupled together electrically in commonor “terminated”. A conductive metal frit that contains one of silver,palladium, platinum, gold and nickel alloys thereof, is placed in thecapacitor holes 118 and along the array side 98 and melted to form thetermination layers 109 and 111 shown in FIGS. 5 and 6. Most commonly,the conductive frit comprises one of silver, silver-palladium alloy ornickel-gold alloy. Alternatively, the capacitor holes 118 and the arrayside 98 may be electroplated with layers of nickel and gold. In stepS212, the capacitor filter array 90 is fired again to densify thetermination layer materials.

[0064]FIG. 12 is a flow chart illustrating the steps of fabricating thefiltered feedthrough assembly 10 from the capacitive filter array 90formed in the steps of FIG. 11, the co-fired metal-ceramic substrate 40formed in the steps of FIG. 10, the ferrule 20, and other components.First, the metal-ceramic substrate 40 is fitted into the ferrule openingand hermetically sealed thereto using the gold or gold alloysubstrate-ferrule braze joint 48 and the externally disposed contactbuttons 70 are sealed into the button cavities 80. Then, the capacitorfilter array 90 is attached to the interior facing surface of themetal-ceramic substrate 40, the capacitor filter conductive paths 110fill the filter holes 108 using reflow solder techniques, and theinternally disposed ground solder joint 130 and the plurality ofinterior contact pads 120 are attached.

[0065] In step S300, the ferrule 20, braze preforms that melt to formthe substrate-ferrule braze joint 48, the metal-ceramic substrate 40,and the externally disposed contact buttons 70 in the button cavities 80are stacked into a braze fixture. Advantageously, these components thatare assembled together in step S300 self center and support one anotherin the braze fixture. This improves the ease of manufacturing andincreases manufacturing batch yields. The stacked assembly is subjectedto brazing temperatures in a vacuum or inert gas furnace in step S302,whereby the braze preforms melt to form the substrate-ferrule brazejoint 48 and the buttons 70 fill the button cavities 80 and adhere tothe braze joints 78. As the assembly cools, the ferrule contracts morethan the co-fired substrate, which puts the co-fired substrate in astate of compression.

[0066] In step S304, the conductive plated pads 82 and the band-shaped,ground plane or trace layer 132 electrically connecting all of thesubstrate ground paths 118 together at each inward facing end thereofare adhered onto the surface 42 as metallization layers. Eachmetallization layer preferably comprises sputtered films, first oftitanium, then of nickel, and finally of gold, so that a three filmmetallization layer is formed in each case.

[0067] In step S306, the discoid capacitive filter array 90, reflowsolder, and the interior contact pads 120 are assembled onto the inwardfacing surfaces of the sub-assembly formed in step S304, and thesecomponents are heated in step S308. The heating causes the solder toflow into and fill the capacitive filter conductive path holes 108 tocomplete the formation of the capacitive filter conductive paths 110 andthe solder pads 128 shown in FIG. 7 and to adhere the internallydisposed bonding pad 120. The solder may be an indium-lead or tin-leadalloy, and the internally disposed bonding pads 120 may be formed ofKovar alloy plated with successive layers of nickel and gold. The finallayer that is exposed to air and that lead wires are bonded or welded toas shown in FIG. 9 preferably is gold.

[0068] In step S310, the ground solder joint 130 is molded around andagainst the filter substrate edge 98 and the band-shaped, ground planeor trace layer 132. The ground solder joint 130 electrically connectsthe three ground electrodes 102, 104, 106 together and to the ferrule 20through the plurality of substrate ground paths 118 and thesubstrate-ferrule braze joint 48. The ground solder joint 130 alsomechanically bonds the discoid capacitive filter array 90 with themulti-layer metal-ceramic substrate 40. Since the ground solder joint130 does not need to provide a hermetic seal, it may be formed of anumber of materials as described above.

[0069] In the sputtering steps of the present invention, a DC magnetronsputtering technique is preferred, but RF sputtering techniques may lesspreferably be employed. A DC magnetron machine that may find applicationin the present invention is an Model 2011 DC magnetron sputtering devicemanufactured by ADVANCED ENERGY of Fort Collins, Colo.

[0070] The pin-to-pin spacing of two single pin or unipolar feedthroughsis typically on the order of 0.125 inches. The above-describedcapacitive filtered feedthrough array provides a spacing of 0.050 inchesbetween adjacent conductive paths. The feedthrough assembly 10 can beformed providing the nine capacitively filter array conductive pathswithin a ferrule 20 that is 0.563 inches long and 0.158 inches wide.

[0071] While the present invention has been illustrated and describedwith particularity in terms of a preferred embodiment, it should beunderstood that no limitation of the scope of the invention is intendedthereby. The scope of the invention is defined only by the claimsappended hereto. It should also be understood that variations of theparticular embodiment described herein incorporating the principles ofthe present invention will occur to those of ordinary skill in the artand yet be within the scope of the appended claims.

1. A filtered feedthrough assembly adapted to be fitted into an openingof a case of an electronic device, the feedthrough assembly having aninternally disposed portion configured to be disposed inside the caseand an externally disposed portion configured to be disposed outside thecase, the assembly comprising: an electrically conductive ferrule havinga ferrule wall adapted to be fitted into the case opening with an innerwall surface defining a centrally disposed ferrule opening and extendingbetween opposed internally and externally facing ferrule sides; amulti-layer, co-fired metal-ceramic substrate having opposed internallyfacing and externally facing substrate sides joined by a commonsubstrate edge, the metal-ceramic substrate further comprising: aplurality of substrate conductive paths extending through the co-firedmetal-ceramic substrate between the internally and externally facinglayer surfaces and electrically isolated from one another; and a furtherplurality of substrate ground paths extending through the co-firedmetal-ceramic substrate between the internally and externally facinglayer surfaces and electrically isolated from the substrate conductivepaths; means for hermetically sealing the common substrate edge to theferrule inner wall within the centrally disposed ferrule opening andelectrically coupling the plurality of substrate ground paths to theferrule; a discoidal capacitive filter array formed of a ceramiccapacitive filter substrate having an internally facing filter substrateside and an externally facing filter substrate side joined by a commonfilter substrate edge, the capacitive filter array substrate furthercomprising: a plurality of filter array conductive paths electricallyisolated from one another and extending between the internally facingfilter substrate side and the externally facing filter substrate side;and a plurality of discoidal capacitor filters each comprising at leastone capacitor active electrode formed within the filter substrate andextending outward from a filter array conductive path and a commoncapacitor ground electrode; means for mechanically joining theexternally facing filter substrate side to the internally facingsubstrate side and electrically joining each filter array conductivepath to a substrate conductive path; and means for electrically couplingthe common capacitor ground electrode of the discoidal capacitor filtersto the plurality of substrate ground paths; whereby the filteredfeedthrough assembly provides a plurality of miniaturized, electricallyisolated, and capacitively filtered, feedthrough conductive paths withlow inductance extending between the internally disposed portion and theexternally disposed portion when the feedthrough assembly is affixedinto an opening in the case of the electronic device
 2. The filteredfeedthrough assembly of claim 1, wherein the case of the electronicdevice and the ferrule are formed of metallic materials amenable tobeing welded together, the electrically conductive ferrule is furthercomprises a welding flange extending outwardly of the ferrule wall awayfrom the ferrule opening for a predetermined distance defining a flangewidth, and the flange formed with a stress relieving thickness forabsorbing stress caused by thermal welding energy applied to the ferruleand flange in the process of welding the flange to the case.
 3. Thefiltered feedthrough assembly of claim 2, wherein the co-firedmetal-ceramic substrate ceramic material comprises one of the groupconsisting essentially of alumina, aluminum nitride, beryllium oxide,and silicon dioxide that has a CTE compatible with the CTE of thematerial of the ferrule.
 4. The filtered feedthrough assembly of claim3, wherein the ferrule is formed of a conductive material selected fromthe group consisting of niobium, titanium, titanium alloys such astitanium-6Al-4V or titanium-vanadium, platinum, molybdenum, zirconium,tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium,ruthenium, palladium, silver, and alloys, mixtures and combinationsthereof.
 5. The filtered feedthrough assembly of claim 1, wherein: themetal-ceramic substrate further comprises a plurality of planar ceramiclayers shaped in a green state to have a layer thickness and a pluralityof substrate conductive path via holes and common ground via holesextending therethrough between an internally facing layer surface and anexternally facing layer surface, the plurality of ceramic layersassembled together and co-fired from the green state to form thesubstrate; each of the plurality of substrate conductive paths extendingthrough the co-fired metal-ceramic substrate between the internally andexternally facing layer surfaces and electrically isolated from oneanother further comprise a plurality of electrically conductive viasextending through via holes of the plurality of layer thicknesses and aplurality of electrically conductive traces formed on certain of theinternally or externally facing layer surfaces such that the conductivetraces join the conductive vias to form each substrate conductive path;and each of the further plurality of substrate ground paths extendingthrough the co-fired metal-ceramic substrate between the internally andexternally facing layer surfaces comprise a plurality of electricallyconductive vias extending through via holes of the plurality of layerthicknesses and at least one conductive trace formed on certain of theinternally or externally facing layer surfaces and extending to thesubstrate edge to enable electrical joinder of the ground vias in commonand to the ferrule through the means for hermetically sealing the commonsubstrate edge to the ferrule inner wall within the centrally disposedferrule opening.
 6. The filtered feedthrough assembly of claim 5,wherein the means for hermetically sealing the common substrate edge tothe ferrule inner wall within the centrally disposed ferrule opening andelectrically coupling the plurality of substrate ground paths to theferrule comprises a substrate-ferrule braze joint formed of a conductivebraze material.
 7. The filtered feedthrough assembly of claim 5, whereineach of the plurality of substrate conductive paths extending throughthe co-fired metal-ceramic substrate between the internally andexternally facing layer surfaces further comprise: a substrate conductorbraze pad on the substrate internally facing side comprising part of themeans for mechanically joining the externally facing filter substrateside to the internally facing substrate side and electrically joiningeach filter array conductive path to a substrate conductive path; asubstrate conductor braze pad on the substrate externally facing side;and an externally disposed bonding button mechanically supported on theexternally facing metal-ceramic substrate side and electricallyconnected with an electrical path of the metal-ceramic substrate throughthe braze pad on the substrate externally facing side.
 8. The filteredfeedthrough assembly of claim 7, wherein the externally disposed bondingbuttons are formed of a conductive material selected from the groupconsisting of niobium, platinum or a platinum-iridium alloy, titanium,titanium alloys such as titanium-6Al-4V or titanium-vanadium,molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium,rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures andcombinations thereof.
 9. The filtered feedthrough assembly of claim 7,wherein the exterior facing surface of the metal-ceramic substrate isformed with a plurality of spaced apart button cavities aligned with theplurality of substrate conductor paths extending through the externallyfacing ceramic layer of the metal-ceramic substrate, each conductor holereceiving a substrate conductor braze pad and an externally disposedbonding button therein.
 10. The filtered feedthrough assembly of claim7, wherein the substrate conductive paths are formed of a conductivepaste applied by screen printing to said ceramic layers in the greenstate to form the traces and fill the via holes, the conductive pasteselected from the group consisting of copper, tungsten, molybdenum andgold.
 11. The filtered feedthrough assembly of claim 7, wherein: eachfilter array conductive path further comprises a filter array holeextending between the internally facing filter substrate side and theexternally facing filter substrate side and through at least onecapacitor active electrode; and the means for mechanically joining theexternally facing filter substrate side to the internally facingsubstrate side and electrically joining each filter array conductivepath to a substrate conductive path comprises reflow solder filling thefilter array holes and mechanically bonded with the substrate conductorbraze pads on the substrate internally facing side, whereby the reflowsolder within each filter array hole forms at least part of a filterarray conductive path.
 12. The filtered feedthrough assembly of claim11, wherein the filter array conductive paths further comprise aplurality of internally disposed bonding pads adhering to the reflowsolder filling the plurality of filter array holes on the internallyfacing side of the capacitive filter array.
 13. The filtered feedthroughassembly of claim 12, wherein the internally disposed bonding pads areformed of a conductive material selected from the group consisting ofcopper, nickel, gold and aluminum and alloys, mixtures and combinationsthereof.
 14. The filtered feedthrough assembly of claim 7, wherein: eachcapacitive filter comprises a plurality of capacitor active electrodesformed within the filter substrate and extending outward from a filterarray conductive path, a further plurality of capacitor groundelectrodes formed within the filter substrate and extending inward fromthe filter substrate edge, and a termination layer overlying the filtersubstrate edge electrically coupling the capacitor ground electrodestogether.
 15. The filtered feedthrough assembly of claim 14, wherein:each filter array conductive path further comprises a filter array holeextending between the internally facing filter substrate side and theexternally facing filter substrate side and through the plurality ofcapacitor active electrodes, and a hole metallization layer within thehole electrically coupling the capacitor active electrodes together; andthe means for mechanically joining the externally facing filtersubstrate side to the internally facing substrate side and electricallyjoining each filter array conductive path to a substrate conductive pathcomprises reflow solder filling the filter array holes and mechanicallybonded with the hole metallization layer and the substrate conductorbraze pads on the substrate internally facing side, whereby the reflowsolder within each filter array hole forms at least part of a filterarray conductive path.
 16. The filtered feedthrough assembly of claim 1,wherein: the filter conductive paths further comprise a plurality ofinternally disposed bonding pads supported along the internally facingfilter substrate side, each internally disposed bonding pad electricallyconducted with a filter array conductive path of the capacitive filterarray; and the substrate conductive paths further comprise a pluralityof externally disposed bonding buttons supported along the externallyfacing metal-ceramic substrate side, each externally disposed bondingbutton electrically conducted with a substrate conductive path.
 17. Thefiltered feedthrough assembly of claim 16, wherein the internallydisposed bonding pads are formed of a conductive material selected fromthe group consisting of copper, nickel, gold and aluminum and alloys,mixtures and combinations thereof.
 18. The filtered feedthrough assemblyof claim 16, wherein the externally disposed bonding buttons are formedof a conductive material selected from the group consisting of niobium,platinum or a platinum-iridium alloy, titanium, titanium alloys such astitanium-6Al-4V or titanium-vanadium, molybdenum, zirconium, tantalum,vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium,palladium, silver, and alloys, mixtures and combinations thereof.
 19. Amethod of manufacturing a filtered feedthrough assembly adapted to befitted into an opening of a case of a hermetically sealed electronicdevice, the feedthrough assembly having an internally disposed portionconfigured to be disposed inside the case and an externally disposedportion configured to be disposed outside the case, the methodcomprising: providing an electrically conductive ferrule having aferrule wall adapted to be fitted into the case opening with an innerwall surface defining a centrally disposed ferrule opening and extendingbetween opposed internally and externally facing ferrule sides; forminga multi-layer, co-fired metal-ceramic substrate having opposedinternally facing and externally facing substrate sides joined by acommon substrate edge, the step of forming the metal-ceramic substratefurther comprising: forming a plurality of substrate conductive pathsextending through the co-fired metal-ceramic substrate between theinternally and externally facing layer surfaces and electricallyisolated from one another; and forming a further plurality of substrateground paths extending through the co-fired metal-ceramic substratebetween the internally and externally facing layer surfaces andelectrically isolated from the substrate conductive paths; hermeticallysealing the common substrate edge to the ferrule inner wall within thecentrally disposed ferrule opening and electrically coupling theplurality of substrate ground paths to the ferrule; forming a discoidalcapacitive filter array formed of a ceramic capacitive filter substratehaving an internally facing filter substrate side and an externallyfacing filter substrate side joined by a common filter substrate edge,the step of forming capacitive filter array substrate further comprisingthe steps of: forming a plurality of filter array conductive pathselectrically isolated from one another and extending between theinternally facing filter substrate side and the externally facing filtersubstrate side; forming a plurality of discoidal capacitor filters eachcomprising at least one capacitor active electrode formed within thefilter substrate and extending outward from a filter array conductivepath and a common capacitor ground electrode; mechanically joining theexternally facing filter substrate side to the internally facingsubstrate side electrically connecting each filter array conductive pathto a substrate conductive path; and electrically connecting the commoncapacitor ground electrode of the discoidal capacitor filters to theplurality of substrate ground paths; whereby the filtered feedthroughassembly provides a plurality of miniaturized, electrically isolated,and capacitively filtered, feedthrough conductive paths with lowinductance extending between the internally disposed portion and theexternally disposed portion when the feedthrough assembly is affixedinto an opening in the case of the electronic device
 20. The method ofclaim 19, wherein the case of the electronic device and the ferrule areformed of metallic materials amenable to being welded together, theelectrically conductive ferrule is further formed with a welding flangeextending outwardly of the ferrule wall away from the ferrule openingfor a predetermined distance defining a flange width, and the weldingflange formed with a stress relieving thickness for absorbing stresscaused by thermal welding energy applied to the ferrule and flange inthe process of welding the flange to the case.
 21. The method of claim20, wherein the co-fired metal-ceramic substrate ceramic material isformed of one of the group consisting essentially of alumina, aluminumnitride, beryllium oxide, and silicon dioxide that has a CTE compatiblewith the CTE of the material of the ferrule.
 22. The method of claim 21,wherein the ferrule is formed of a conductive material selected from thegroup consisting of niobium, titanium, titanium alloys such astitanium-6Al-4V or titanium-vanadium, platinum, molybdenum, zirconium,tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium,ruthenium, palladium, silver, and alloys, mixtures and combinationsthereof.
 23. The method of claim 19, wherein the metal-ceramic substrateis formed by the further method of: forming a plurality of planarceramic layers shaped in a green state to have a layer thickness;forming a plurality of substrate conductive path via holes and groundpath via holes extending therethrough between an internally facing layersurface and an externally facing layer surface; filling conductive pathand ground path via holes with conductive material; forming conductivepath traces and ground traces on selected ones of the internally andexternally facing layer surfaces; assembling and laminating theplurality of ceramic layers together; punching the outer dimensions ofthe assembled and laminated plurality of ceramic layers; co-firing theassembled and laminated ceramic layers from the green state to form thesubstrate having the opposed internally facing and externally facingsubstrate sides joined by a common substrate edge; and machining andpolishing the common substrate edge to enable to enable electricalconnection of the ground vias in common and to the ferrule in the stepof hermetically sealing the common substrate edge to the ferrule innerwall within the centrally disposed ferrule opening.
 24. The method ofclaim 23, wherein the further method of hermetically sealing the commonsubstrate edge to the ferrule inner wall within the centrally disposedferrule opening and electrically coupling the plurality of substrateground paths to the ferrule comprises forming a substrate-ferrule brazejoint of a conductive braze material.
 25. The method of claim 23,wherein the plurality of substrate conductive paths extending throughthe co-fired metal-ceramic substrate between the internally andexternally facing layer surfaces are formed by the further stepscomprising: placing a substrate conductor braze pad on the substrateinternally facing side over an exposed conductive trace or via of eachconductive path; placing a bonding button over each exposed braze pad;and applying heat to melt the braze pads and to thereby mechanically andelectrically join the bonding button with the substrate conductive path.26. The method of claim 25, wherein the externally disposed bondingbuttons are formed of a conductive material selected from the groupconsisting of niobium, platinum or a platinum-iridium alloy, titanium,titanium alloys such as titanium-6Al-4V or titanium-vanadium,molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium,rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures andcombinations thereof.
 27. The method of claim 23, further comprising: inthe green state and prior to assembling and laminating the ceramiclayers, forming a plurality of spaced apart button cavities extendingthrough the externally facing ceramic layer of the metal-ceramicsubstrate located to be aligned with the plurality of substrateconductor paths through the remaining ceramic layers; and wherein theplurality of substrate conductive paths extending through the co-firedmetal-ceramic substrate between the internally and externally facinglayer surfaces are formed by the further method comprising: placing asubstrate conductor braze pad within each button cavity of the substrateinternally facing side and over an exposed conductive trace or via ofeach conductive path; placing a bonding button in each button cavityover each braze pad; and applying heat to melt the braze pads and tothereby mechanically and electrically join the bonding button with thesubstrate conductive path.
 28. The method of claim 23, wherein aconductive paste material selected from the group consisting of copper,tungsten, molybdenum and gold is used in the steps of filling conductivepath and ground path via holes and forming conductive path traces andground traces and is applied by screen printing to said ceramic layersin the green state.
 29. The method of claim 23, wherein: the capacitivefilter array is formed through the further method of extending a filterarray hole between the internally facing filter substrate side and theexternally facing filter substrate side and through at least onecapacitor active electrode; and the method of mechanically joining theexternally facing filter substrate side to the internally facingmetal-ceramic substrate side and electrically joining each filter arrayconductive path to a substrate conductive path comprises the steps of:placing a substrate conductor braze pad on the externally facingmetal-ceramic substrate side over an exposed conductive trace or via ofeach conductive path; placing the internally facing filter substrateside against the externally facing metal-ceramic substrate side with thefilter array holes aligned with the substrate conductor braze pads onthe externally facing metal-ceramic substrate side placing soldermaterial in the filter array holes to form a sub-assembly; and heatingthe sub-assembly to reflow solder fill the filter array holes andmechanically bond with the substrate conductor braze pads on thesubstrate internally facing side, whereby the reflow solder within eachfilter array hole forms at least part of a filter array conductive path.30. The method of claim 29, further comprising the method of placing aninternally disposed bonding pad against the solder placed in each of theplurality filter array holes whereby the plurality of internallydisposed bonding pads adhere to the reflow solder filling the pluralityof filter array holes on the internally facing side of the capacitivefilter array.
 31. The method of claim 30, wherein the internallydisposed bonding pads are formed of a conductive material selected fromthe group consisting of copper, nickel, gold and aluminum and alloys,mixtures and combinations thereof.
 32. The method of claim 29, whereinthe capacitive filter array is formed through the further method of:forming a plurality of capacitor active electrodes the filter substrateand extending outward from a filter array conductive path, applying ahole metallization layer within the hole electrically coupling thecapacitor active electrodes together; forming a further plurality ofcapacitor ground electrodes formed within the filter substrate andextending inward from the filter substrate edge, applying an edgemetallization layer overlying the filter substrate edge electricallycoupling the capacitor ground electrodes together, whereby each filterarray hole is formed to extend between the internally facing filtersubstrate side and the externally facing filter substrate side andthrough the plurality of capacitor active electrodes.
 33. The method ofclaim 19, wherein the method of mechanically joining the externallyfacing filter substrate side to the internally facing substrate side andelectrically joining each filter array conductive path to a substrateconductive path comprises reflow soldering the filter array conductivepath with the substrate conductive path
 34. The method of claim 19,further comprising a further method of: providing a plurality ofinternally disposed bonding pads supported along the internally facingfilter substrate side, each internally disposed bonding pad electricallyconducted with a filter array conductive path of the capacitive filterarray; and providing a plurality of externally disposed bonding buttonssupported along the externally facing metal-ceramic substrate side, eachexternally disposed bonding button electrically conducted with asubstrate conductive path.
 35. The method of claim 34, wherein theinternally disposed bonding pads are formed of a conductive materialselected from the group consisting of copper, nickel, gold and aluminumand alloys, mixtures and combinations thereof.
 36. The method of claim34, wherein the externally disposed bonding buttons are formed of aconductive material selected from the group consisting of niobium,platinum or a platinum-iridium alloy, titanium, titanium alloys such astitanium-6Al-4V or titanium-vanadium, molybdenum, zirconium, tantalum,vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium,palladium, silver, and alloys, mixtures and combinations thereof.
 37. Afiltered feedthrough assembly adapted to be fitted into an opening of acase of an electronic device, the feedthrough assembly having aninternally disposed portion configured to be disposed inside the caseand an externally disposed portion configured to be disposed outside thecase, the assembly comprising: an electrically conductive ferrule havinga ferrule wall adapted to be fitted into the case opening with an innerwall surface defining a centrally disposed ferrule opening and extendingbetween opposed internally and externally facing ferrule sides; amulti-layer, co-fired metal-ceramic substrate having opposed internallyfacing and externally facing substrate sides joined by a commonsubstrate edge, the metal-ceramic substrate further comprising aplurality of substrate conductive paths extending through the co-firedmetal-ceramic substrate between the internally and externally facinglayer surfaces and electrically isolated from one another; means forhermetically sealing the common substrate edge to the ferrule inner wallwithin the centrally disposed ferrule opening and electrically couplingthe plurality of substrate ground paths to the ferrule; a discoidalcapacitive filter array formed of a ceramic capacitive filter substratehaving an internally facing filter substrate side and an externallyfacing filter substrate side joined by a common filter substrate edge,the capacitive filter array substrate further comprising: a plurality offilter array conductive paths electrically isolated from one another andextending between the internally facing filter substrate side and theexternally facing filter substrate side each formed of reflow solderfilling a; filter array hole; and a plurality of discoidal capacitorfilters each comprising at least one capacitor active electrode formedwithin the filter substrate and extending outward from a filter arrayconductive path and a common capacitor ground electrode; means formechanically joining the externally facing filter substrate side to theinternally facing substrate side and electrically joining each filterarray conductive path to a substrate conductive path comprising thereflow solder forming the plurality of filter array conductive paths;and means for electrically coupling the common capacitor groundelectrode of the discoidal capacitor filters to the ferrule; whereby thefiltered feedthrough assembly provides a plurality of miniaturized,electrically isolated, and capacitively filtered, feedthrough conductivepaths extending between the internally disposed portion and theexternally disposed portion when the feedthrough assembly is affixedinto an opening in the case of the electronic device